Rate constants for the reaction between a secondary alkyl radical and two different sulfonyl azides were determined using bimolecular competing radical reactions. The rates of azidation were determined by competition with hydrogen atom transfer from tris(trimethylsilyl)silane ((TMS)3SiH) of the 4-phenylcyclohexyl radical. 3-Pyridinesulfonyl azide and trifluoromethanesulfonyl azide were found to have rate constants for azidation of 2 × 105 M–1 s–1 and 7 × 105 M–1 s–1 at 80°C, respectively.